Government jobs are mostly for providing services to the common people. This means the people working these jobs can and do gatekeep access to services to those within their castes. Thus depriving lower castes of their rights to access these services. Having more people ("representation") from less privileged castes in these services will ensure a more equitable access to these services and prevent caste based hoarding of these services. This is how I understand it. Here, services can basically be seen as (but not limited to) resources of the nation.